Epoxy phosphate ester resin, its production and coating composition containing the resin

ABSTRACT

The present invention provides a process for preparing an epoxy phosphate ester resin, which comprises (1) reacting an epoxy resin having an average of greater than one vicinal epoxy group with a phosphoric acid source material to obtain an epoxy phosphate ester; and (2) further reacting the obtained epoxy phosphate ester with a phosphoric acid source material. The present invention provides epoxy phosphate ester resins obtained by the above process, which exhibit good water-solubility. The coating compositions containing such epoxy phosphate ester resin show good coating properties such as good corrosion resistance, chemical resistance, heat resistance and flexibility.

TECHNICAL FIELD

The present invention relates to a water-soluble epoxy phosphate esterresin which can be used as a water-borne coating material, itsproduction process and a coating composition containing the resin.

BACKGROUND ART

Epoxy resins have been used in a wide variety of applications such ascoating applications, for example, because of their superiority incorrosion resistance, chemical resistance and flexibility. In order toimprove workability, the epoxy resins are usually diluted with anorganic solvent to decrease their viscosities.

Recently, various laws and regulations regarding use of organicsolvents, such as organic solvent intoxication prevention regulationsand fire regulations, have become more stringent. Because of suchregulations, it is desired to make epoxy resins for coating compositionswater soluble or water dispersible. Several attempts have been made tomodify conventional epoxy resins which per se are not water soluble. Forexample, self-dispersion type epoxy resins modified with an acrylicresin have been proposed and disclosed in Japanese Patent ApplicationLaid-Open Gazettes Nos. Sho 55-003,481 and Sho 58-198,513.

Further, for simplification of steps, studies have been carried out tomake an epoxy resin per se water dispersible. For example, in JapanesePatent Application Laid-Open Gazette No. Hei 2-212,570, an epoxy resinis reacted with phosphoric acid to make the resin water dispersible.However, phosphoric acid has three hydroxyl groups and thus triesters ofphosphoric acid are easily formed. For this reason, to obtain an epoxyphosphate ester resin having low viscosity and good dispersionstability, excess amounts of phosphoric acid must be employed.Therefore, unreacted phosphoric acid may remain in the resin productresulting in problems such as blushing of resultant coatings.

Japanese Patent Publication Gazette No. Hei 1-055,299 discloses an epoxyphosphate ester resin prepared by reacting an epoxy resin withphosphoric acid, and then hydrolyzing the phosphoric acid modified epoxyresin for monoesterification. The resultant resin per se can be madewater dispersible. However, the resins have unduly large particle sizewhen dispersed in water, resulting in poor dispersion stability.Accordingly, if the amount of organic solvent used is restricted,sufficient dispersion stability cannot be obtained. In particular, inpaints prepared using an aromatic epoxy resin, a completely transparentaqueous solution cannot be obtained. In the case of relatively lowmolecular weight epoxy resins having a weight average molecular weightof 340 to 4,000, there is a problem that they are difficult to hydrolyzeand their viscosities increase when dispersed in water.

In view of the deficiencies of the prior art described above, it wouldbe desirable to provide an epoxy phosphate ester resin which exhibitsgood water-solubility, and its production process.

It would also be desirable to provide a coating composition having goodcoating properties such as a good anti-rust property and goodflexibility.

SUMMARY OF INVENTION

According to the present invention, there is now provided a process forpreparing an epoxy phosphate ester resin, which comprises (1) reactingan epoxy resin having an average of greater than one vicinal epoxy groupwith a phosphoric acid source material to obtain an epoxy phosphateester; and (2) further reacting the obtained epoxy phosphate ester witha phosphoric acid source material.

Another aspect of the present invention pertains to an epoxy phosphateester resin prepared by the above process.

Another aspect of the present invention relates to a coating compositioncomprising:

(a) the epoxy phosphate ester resin obtained as above;

(b) an acrylic resin and/or a polyester resin, miscible with the epoxyphosphate ester resin;

(c) at least one curing agent; and

(d) water and/or an organic solvent.

According to the process of the present invention, water-soluble epoxyphosphate ester resins having low viscosity can be obtained whilerestricting the amount of free phosphoric acid, diesters of phosphoricacid and triesters of phosphoric acid to a minimum level.

The water-soluble resins of the present invention can be used to form amore stable aqueous solution when compared with conventional epoxyphosphate ester resin. The water-borne coating compositions according tothe present invention, provides a resultant coating film with improvedcorrosion resistance and flexibility as compared with a conventionalpaint such as an acrylic resin-based paint. Accordingly, the coatingcompositions of the present invention can be effectively used,particularly, in the fields of coating applications such as spraycoating and roll coating.

DETAILED EXPLANATION OF THE INVENTION

In the present invention, any known epoxy resins having an average ofmore than one epoxy group per molecule, can be used. Suitable epoxyresins include, for example, those having an epoxy equivalent weight offrom 170 to 3,500, more suitably from about 175 to 1,000, and a weightaverage molecular weight of from 340 to 18,000, more suitably from 340to 5,000. Preferred epoxy resins which can be used herein, are thosehaving two vicinal epoxy groups such as diglycidyl ethers of bisphenolA, bisphenol K, bisphenol F, bisphenol S, bisphenol AD, aliphaticphenols and mixtures thereof. The most preferred epoxy resin arediglycidyl ethers of bisphenol A and diglycidyl ethers of aliphaticphenols.

In the present invention, the epoxy resins are not limited to theabove-mentioned epoxy resins, but include any known epoxy resins. Suchepoxy resins are well described in, for example, U.S. Pat. Nos.4,289,812, 4,397,970, 4,868,059 and 5,070,174, and "The Handbook ofEpoxy Resins" by H. Lee and K. Neville, published in 1967 byMcGraw-Hill, New York, all of which are incorporated herein byreference.

As commercially available epoxy resins, D.E.R.™ 331L; D.E.R.™ 383J;D.E.R.™ 661; D.E.R.™ 664; D.E.R.™ 732; and D.E.N.™ 438 (trademarks ofThe Dow Chemical Company) resins, available from The Dow ChemicalCompany, can be used.

The epoxy resins which can be used in the present invention may beprepared by the reaction of a commercially available epoxy resin and aphenolic compound having an average of more than one hydroxyl group. Inthis case, the epoxy resin and the phenolic compound may be used in anamount to provide an epoxy:phenolic component ratio by weight ofpreferably from 60:40 to 99:1, more preferably from 75:25 to 99:1.

Also, if the amount of the phenolic compound used exceeds 40 percent byweight, the next reaction, i.e., phosphorylation is difficult toconduct.

In the reaction between the epoxy component and the phosphoric acidcomponent, according to the present invention, any known catalyst can beused. Such known catalysts include, for example, imidazoles such as2-methylimidazole; tertiary amines such as triethylamine, tripropylamineand tributylamine; phosphonium salts such as ethyltriphenylphosphoniumchloride, ethyltriphenylphosphonium bromide andethyltriphenylphosphonium acetate-acetic acid complex; and ammoniumsalts such as benzyltrimethylammonium chloride andbenzyltrimethylammonium hydroxide.

In addition, known catalysts other than the above-mentioned catalystscan be used. Such catalysts include those described in, for example,U.S. Pat. Nos. 4,289,812; 4,397,970 and 4,868,059, all of which areincorporated herein by reference.

In the present invention, acidic catalysts are preferable. The amount ofthe catalysts used generally ranges from 0.001, preferably 0.01 to 1,preferably to 0.3 percent by weight, based on the total solid weight ofthe reaction mixture.

In the present invention, the above-mentioned epoxy resin is reactedwith a phosphoric acid source material and the reaction product obtainedis further reacted with a phosphoric acid source material. The obtainedproduct is then subjected to hydrolysis treatment to produce an epoxyphosphate monoester resin.

Phosphoric acid source materials which can be employed in the presentinvention include, for example, 100 percent phosphoric acid, thesemi-hydrate (2H₃ PO₄.H₂ O) and aqueous solutions containing at least 18weight percent HP₃ O₄ (at least 1 mole H₃ PO₄ per 25 moles of water).The various condensed forms (polymeric, partial anhydrides) ofphosphoric acid, pyrophosphoric acid, orthophosphoric acid andtriphosphoric acid can also be used. Preferred are phosphoric acidhaving an H₃ PO₄ concentration of from 85 to 120 percent, and morepreferred are superphosphoric acids having an H₃ PO₄ concentration offrom 105 to 116 percent.

For the reaction of the epoxy component and the phosphoric acidcomponent, the phosphoric acid source material may be added dropwise tothe epoxy component at, for example, 50° C. to 150° C. for a period offrom 1, preferably 5 to 110, preferably to 15 minutes. After thedropwise addition, the reaction mixture may be heated and stirred for 1to 120 minutes. If desired, these procedures may be repeated as manytimes as necessary.

Water-dispersible epoxy phosphate ester resins can be obtained even ifthe whole amount of phosphoric acid source material for the two-stepreaction is simultaneously reacted in a single step with an epoxy resin.However, in such a case the reaction products have high viscosity andalso contain unreacted phosphoric acid, triesters and diesters ofphosphoric acid, resulting in poor stability when dispersed in anaqueous solution.

In the present invention, when producing high molecular weight epoxyphosphate ester resins, it is possible to perform a uniform reaction bydecreasing the viscosity of the reaction mixture with an organic solventto improve stirring efficiency.

Suitable solvents for use herein include organic solvents having goodcompatibility with an epoxy resin and a boiling point higher than 110°C., especially higher than 140° C., Examples of the organic solventsused herein are glycol type solvents such as ethylene glycol andpropylene glycol; glycol monoether type solvents such as ethylene glycolmonoethyl ether, ethylene glycol monobutyl ether, dipropylene glycolmethyl ether, diethylene glycol butyl ether, propylene glycol n-butylether; acetate type solvents such as propylene glycol monomethyl etheracetate, butyl acetate and propylene glycol methyl ether acetate;alcohol type solvents such as n-butanol, amyl alcohol and cyclohexanol;ketone type solvents such as cyclohexanone and diisobutyl ketone; andaromatic solvents such as xylene and SOLVESSO™ 100 (supplied by ExxonChemical). Of these solvents, a glycol type solvent and an alcohol typesolvent are especially preferred. These solvents can be used singly oras a mixture of two or more thereof. The non-volatiles concentration ofthe diluted reaction system is preferably from 50 to 100 percent, basedon the total reaction mixture. The higher solids concentration ispreferable within the viscosity range where the reaction mixture is notgelled.

In the reaction between the above-mentioned phosphoric acid componentand the above-mentioned epoxy component, in the first reaction step anepoxy resin may be reacted with a phosphoric acid source material in anamount to provide from 0.2 to 0.4, preferably from 0.25 to 0.35 hydroxylgroup per epoxy group; and in the second reaction step the obtainedepoxy phosphate ester is reacted with a phosphoric acid source materialin an amount to provide from 0.05 to 0.4, preferably from 0.05 to 0.20hydroxyl group per epoxy group.

More specifically, in the case of using 100 percent phosphoric acid, theamount of the phosphoric acid source material used for one reaction maypreferably range from 0.1 to 6.0 percent by weight, more preferably from0.3 to 5.5 percent by weight, most preferably from 0.4 to 4.8 based onthe total solid content of the reaction mixture. If the amount of thephosphoric acid source material used is less than 0.1 percent by weight,the resultant resins have a large amount of unreacted epoxy groups,resulting in increased viscosity or poor dispersion stability whendispersed in water. If the amount of unreacted epoxy groups exceeds 6.0percent by weight, gelation may occur during the reaction or freephosphoric acid will be formed during the next reaction step. These aredisadvantageous and free phosphoric acid will cause blushing when acoating of the resultant resin is subjected to retort treatment.

The phosphoric acid source materials per se can be added dropwise.However, it is effective to use the phosphoric acid source materialdiluted with a hydroxylic solvent such as the above-mentioned glycolmonoether type solvent or a mixture thereof. The use of the hydroxylgroup-containing solvents prevents self-condensation of the phosphoricacid source materials, resulting in a more uniform reaction. Thesesolvents can be used in an amount to provide a molar ratio of thesolvent to the phosphoric acid source material of at least 2:1,preferably at least 4:1.

The epoxy phosphate ester resins prepared as above are mainly in theform of triesters or diesters, and thus can be changed to monoesters bysubjecting them to partial hydrolysis to reduce them to monoesters.Monoesterification reduces the viscosity of the resultant hydrolyzedmodified epoxy phosphate ester resin to make handling easier.

Further, the phosphate groups existing at the end of molecules canprovide good corrosion resistance inherently possessed by the phosphoricacid. Further, the phosphoric acid residues may catalyze curing of theresultant coated film and provide flexibility to the coated film. Thehydrolyzed, modified epoxy phosphate ester resins may contain a smallquantity of diesters, triesters and free phosphoric acid in addition tomonoesters, but normally contain almost no epoxy groups.

In the process of the present invention, the epoxy phosphate esterresins can be made water-soluble by adding at least one amine compoundto the resin to adjust its pH to between 6 and 11, adding dropwisewater, and then stirring the obtained product. If the pH of the adjustedepoxy phosphate ester resin is outside the pH range of 6 to 11, theresultant solution may have poor stability.

Suitable amine compounds which can be used in the present inventioninclude those described in U.S. Pat. Nos. 4,289,812 and 4,397,970; forexample, alkanol amines such as N,N-dimethylethanol amine. Particularlypreferred is an amine mixture prepared by mixing N,N-dimethylethanolamine and diethanol amine at a weight ratio of between 50:50 and 70:30.

In the present invention, neutralization can be effected at roomtemperature. However, if the reaction mixture has high viscosity due toits high solids content or use of resins of high molecular weight, thereaction mixture can be heated at a temperature below the boiling pointof the amine compound used.

In the present invention, the epoxy phosphate ester resin may beincorporated with, for example, an acrylic resin and/or a polyesterresin, a curing agent, water and/or an organic solvent to prepare acoating composition.

Acrylic resins which can be used in the present invention include anyacrylic resin known as a coating material, such as a polymer of alkylacrylate or methacrylate and a monomer copolymerizable therewith.Suitable alkyl (meth)acrylate polymers include, for example, thoseprepared from methyl (meth)acrylate, ethyl (meth)acrylate, butyl(meth)acrylate and 2-ethylhexyl (meth)acrylate and a monomercopolymerizable with these esters. Suitable copolymerizable monomersused herein include, for example, (meth)acrylic acid, maleic acid,itaconic acid, 2-hydroxyethyl (meth)acrylate, hydroxypropyl(meth)acrylate, acryl-amide, N-methylol acryl-amide, styrene,vinyltoluene, acrylonitrile and vinylacetate.

Polyester resins which can be used in the present invention includepolyester resins known as coating materials, which are prepared from asuitable alcohol component and a suitable acid component. Suitablealcohol components include, for example, ethylene glycol, diethyleneglycol, polyethylene glycol, propylene glycol, dipropylene glycol,polypropylene glycol, neopentyl glycol, butanediol, 1,5-pentanediol,1,6-hexanediol, 1,4-cyclohexanedimethanol, glycerol, anthrol,trimethylolethane, hexanetriol and pentaerythritol. Suitable acidcomponents include, for example, phthalic acid, tetrahydrophthalic acid,hexahydrophthalic acid, trimellitic acid, pyromellitic acid, isophthalicacid, terephthalic acid, maleic acid, fumaric acid, itaconic acid,adipic acid, azelaic acid, sebacic acid, succinic acid and anhydrides ofthese acids.

Curing agents which can be incorporated into the composition forsolvent-borne coatings according to the present invention include, forexample, amino resins such as melamine-formaldehyde andurea-formaldehyde; alkyl-etherified amino resins such as those preparedfrom the etherification of the above amino resins with lower alcoholssuch as methanol or ethanol; polyisocyanates such as isophoronediisocyanate and m-xylene diisocyanate; blocked isocyanates such asthose formed by introducing blocking agents such as alcohols, includingmethanol, or phenols, including cresol, into the above polyisocyanates;and alkyl-etherified phenol resins such as an aryl ether monomethylolphenol. For water-borne coatings, any known water-soluble curing agentscan be used.

The epoxy resins of the present invention can be used as raw materialsfor water-borne coating compositions, which are considered preferablefrom an environmental view point, as well as raw materials forsolvent-borne coating compositions.

The epoxy phosphate ester resins of the present invention can beincorporated with water and known water-soluble curing agents to preparea water-borne coating composition.

The epoxy phosphate ester resins of the present invention can also beused to prepare a solvent-borne coating composition. Suitable organicsolvents which can be used as diluent to adjust viscosity include, forexample, the above-mentioned glycol-type solvents, glycol monoether-typesolvents, alcohol-type solvents, aromatic-type solvents and ketone-typesolvents (such as methyl ethyl ketone, methyl isobutyl ketone andcyclohexanone). These solvents can be used alone or in combination.

The epoxy phosphate ester resins of the present invention can be used incombination with a known epoxy resin as long as the resin mixture keepsgood performance derived from the epoxy phosphate ester resins.

The preferable component ratio of a coating composition of the presentinvention is as follows:

(a) from 1, preferably 5 to 30, preferably 20 percent by weight of anepoxy phosphate ester resin;

(b) from 50, preferably 70 to 90, preferably 80 percent by weight of anacrylic resin and/or a polyester resin; and

(c) from 10, preferably 15 to 30, preferably 20 percent by weight of acuring agent for Components (a) and (b).

To the above composition, (d) water and/or an organic solvent may beadded to provide a volatiles content of, for example, from 10,preferably 15 to 80, preferably 40 percent by weight.

If desired, these coating compositions may comprise an appropriateamount of a pigment, plasticizer, coloring agent, flow modifier and/orcuring accelerator.

EXAMPLES AND COMPARATIVE EXAMPLES

The present invention will now be described in more detail withreference to the following Examples and Comparative Examples, which arenot to be construed as limiting the invention.

In the Examples and Comparative Examples, all of the percentages andparts are by weight unless otherwise indicated.

Example 1

A reaction vessel equipped with a condenser was charged with 777 partsof a diglycidyl ether of bisphenol A (D.E.R.™ 331 resin: trademark ofThe Dow Chemical Company), 323 parts of bisphenol A and 0.2 parts of acatalyst, a 70 percent methanol solution of ethyltriphenyl phosphoniumacetate-acetic acid complex. The reaction was carried out in a nitrogencurrent at 175° C. for 1 hour.

A mixed solvent containing DOWANOL™ PM (propylene glycol methyl ether)and DOWANOL™ DPM (dipropylene glycol methyl ether) (1:1 weight ratio)was then added to the reaction mixture to adjust the solidsconcentration to 90 percent and to cool the reaction mixture to 125° C.Then, 20 parts of a solution prepared by diluting superphosphoric acidhaving a concentration of 105 percent in 4 times as many moles of thesame mixed solvent (DOWANOL™ PM and DOWANOL™ DPM 1:1 weight ratio) asphosphoric acid, were added dropwise to the reaction product over aperiod of 30 minutes. To the reaction product obtained, 20 parts of thesame superphosphoric acid solution were added in the same way as abovefor further reaction, under the same conditions.

Then, 20 parts of water were added to the reaction product forhydrolysis to obtain an epoxy phosphate monoester resin. The epoxyphosphate ester resin obtained as above was subjected to neutralizationwith dimethylethanol amine, and then incorporated into water to preparea transparent aqueous solution having a volatiles content of 34.2percent and pH of 7.3.

To the aqueous solution of the epoxy phosphate ester resin obtained, asindicated in Table 1, an acrylic resin and a melamine curing agent wereadded. Further, to the mixture, deionized water was added for dilutionto prepare a coating composition having volatiles content of 25 percent.

Example 2

In the fashion described in Example 1 and except as otherwise stated,using the same reactants, amounts and conditions, 407 parts D.E.R.™ 732aliphatic diglycidyl ether resin supplied by The Dow Chemical Companyand 43 parts bisphenol A were reacted in the presence of 0.6 parts ofthe same phosphonium-acid complex catalyst.

The reaction system was cooled to 125° C. and 9 parts of the same 1:4superphosphoric acid:mixed solvent solution were added dropwise over 30minutes and then 9 parts of the superphosphoric acid solution werefurther added. The reaction product was hydrolyzed with 10 parts water,subjected to the amine neutralization and diluted with water to atransparent 32.2 percent volatiles solution of pH 7.5.

As in Example 1, a coating composition, indicated in Table 1, of 25percent volatiles content was prepared.

Example 3

In the same fashion, 100 parts of D.E.R.™ 331 diglycidyl ether suppliedby The Dow Chemical Company was reacted by dropwise addition of 4.8parts of the superphosphoric acid solution over 20 minutes at 125° C. Tothe resulting product at 125° C., another 4.8 parts of thesuperphosphoric acid solution were added dropwise and then 3 parts waterwere added to hydrolyze the product. Neutralization with thedimethylethanol amine and dilution with water was carried out to yield atransparent solution of pH 7.5 having 35.6 percent volatiles content.

As in Example 1, a coating composition, indicated in Table 1, of 25percent volatiles content was prepared.

Example 4

A coating composition was prepared in the same way as in Example 3except that the kind of acrylic resin was changed as indicated in Table1.

Reference Example

A reaction vessel equipped with a condenser was charged with 388 partsof an aliphatic diglycidyl ether (D.E.R.™ 331: trademark of The DowChemical Company), 112 parts of bisphenol A and 0.1 parts of a 70percent methanol solution of ethyltriphenyl phosphonium acetate-aceticacid complex. The reaction was carried out in a nitrogen current at 175°C. for 1 hour. Thereafter, a mixed solvent containing DOWANOL™ PM andDOWANOL™ DPM (1:1 weight ratio) was added to the reaction mixture toadjust a solid concentration to 70 percent and to cool the reactionmixture to 125° C.

Then, a solution prepared by diluting 10 parts of superphosphoric acidhaving a concentration of 105 percent in an amount 4 times as much molesof a mixed solvent containing DOWANOL™ PM and DOWANOL™ DPM (1:1 weightratio) as that of superphosphoric acid, were added dropwise to thereaction product over a period of 30 minutes for reaction.

Then, 10 parts of water were added to the reaction product obtained forhydrolysis to obtain an epoxy phosphate ester resin. The epoxy phosphateester resin obtained was subjected to neutralization withdimethylethanol amine, and then incorporated with water. However, theviscosity of the suspension liquid increased and it became a white solidproduct.

From the results of this Reference Example, it was found that theproducts obtained through a single reaction with superphosphoric acidexhibit poor water-solubility compared with those obtained through atwo-step reaction with superphosphoric acid as in the present Examples1-4.

Comparative Example 1

The emulsion type acrylic resin (AR-1) used in Examples 1 to 3 wasincorporated with a melamine curing agent as indicated in Table 1. Tothe mixture, deionized water was added for dilution of the volatilescontent to 25 percent, to prepare a coating composition.

Comparative Example 2

The emulsion type acrylic resin (AR-2) used in Example 4 wasincorporated with a melamine curing agent as indicated in Table 1.Deionized water was added to the mixture for dilution so that thevolatiles content became 25 percent, to prepare a coating composition.

Next, a coating composition consisting of an acrylic resin and a curingagent was prepared as comparison.

                  TABLE 1                                                         ______________________________________                                        Kind of Resin      Component Ratios (wt. %)                                   Epoxy         Acrylic  Epoxy Resin/                                                                             CYMEL™                                   Resin         Resin    Acrylic Resin                                                                            303                                         ______________________________________                                        Ex. 1  Bis A Based                                                                              AR-1     70/15    15                                        Ex. 2  Aliphatic  AR-1     70/15    15                                        Ex. 3  Bis A Based                                                                              AR-1     70/15    15                                        Ex. 4  Bis A Based                                                                              AR-2     70/15    15                                        Comp.  --         AR-1      0/85    15                                        Ex. 1                                                                         Comp.  --         AR-2      0/85    15                                        Ex. 2                                                                         ______________________________________                                         AR-1: Emulsion type acrylic resin having a MW of 20,000.                      AR2: Watersoluble acrylic resin having a MW of 9,600.                         CYMEL™ 303: Melamine hardener supplied by MitsuiCyanamid.             

EXPERIMENT

The coating compositions prepared as above were coated on a tin-platedsteel sheet, and heated to 180° C. for 10 minutes for heat curing. Then,the properties of the resultant coated films were evaluated. In theexperiment, pigment was not used in order to evaluate the properties ofthe resins themselves.

The evaluation methods used in the experiment are as follows.

T-Bend Test

A coated specimen (3 cm×3 cm) is bent so that the coated surface appearsoutside, and a plurality of tin plates (spacer) having the samethickness as that of the specimen are inserted inside of the bentspecimen. Then, the bent specimen is pressed. The bent specimen isre-pressed after the number of the spacers is reduced, one by one, untila crack occurs in the coated film. The minimum number of the spacerswhere a crack did not occur is regarded as an index of flexibility.

Xylene Double Rubbing Test

A specimen is subjected to a rubbing test using a rubbing tester withxylene at a load of 2 pounds. The maximum number of rubbing is set as100 times.

Boiling Water Resistance

Pencil hardness is measured before and after a coated specimen isimmersed in a boiling water for a period of 2 hours. The pencil hardnesstest is conducted in accordance with JIS K-5400.

Salt Spray Test

In accordance with JIS K-5400, width of rust formed 500 hours afterspraying is measured.

The results of the testing, carried out on coatings prepared from thecoating compositions described above, are shown in Table 2.

                  TABLE 2                                                         ______________________________________                                                         Xylene             Salt Spray                                                 Double   Boiling Water                                                                           Test                                      Example/ T-Bend  Rubbing  Resistance                                                                              (500 hrs, Rust                            Comp. Ex.                                                                              Test    Test     (Before/After)                                                                          width in mm)                              ______________________________________                                        Example 1                                                                              1T      >100     H/HB      1.0                                       Example 2                                                                              1T      >100     H/HB      2.0                                       Example 3                                                                              2T      >100     H/HB      2.0                                       Example 4                                                                              2T      >100     H/H       3.5                                       Comp. Ex. 1                                                                            2T      >100     H/HB      4.0                                       Comp. Ex. 2                                                                            3T      >100     H/B       5.5                                       ______________________________________                                    

Apparent from the results, as shown in Table 2, it was found that thewater-soluble epoxy resins of the present invention show goodflexibility and corrosion resistance without sacrificing otherproperties such as chemical resistance and heat resistance.

INDUSTRIAL APPLICABILITY

The epoxy phosphate ester resins of the present invention exhibit animproved curing time, corrosion resistance, chemical resistance,flexibility and hardness, and can provide a transparent aqueous solutionwhen the solution is neutralized. The resins exhibit good stability whendissolved in water.

Accordingly, the coating compositions of the present invention can beeffectively used in coating applications such as spray coating and rollcoating. Particularly, the coating compositions show good performance inthe fields of can coating, coil coating and post coating.

More specifically, the coating compositions according to the presentinvention can be effectively used as coating materials on steel basedplates or sheets such as a tin-plated steel (TPS) sheet, tin-free steel(TFS) sheet and galvanized steel sheet; and non-steel based plates orsheets such as an aluminum sheet.

Also, the resin compositions of the present invention can be effectivelyused as primers for substrates. In this case, conventional coatingmaterials may be coated thereon as top coating layers. Such coatingmaterials for top coatings include, for example, an alkyd resin-basedpaint, polyester resin-based paint, thermosetting acrylic resin-basedpaint, vinyl resin-based paint and silicon resin-based paint.

Further, the resin compositions of the present invention can be used ascoating materials for top coating when an aqueous solution of the resincomposition is blended with a water-soluble or water-dispersible acrylicresin or polyester resin. Therefore, the epoxy resins of the presentinvention can be used as additive for an acrylic resin-based paint or apolyester resin-based paint, in which an epoxy resin was not previouslyused.

I claim:
 1. A process for preparing an epoxy phosphate ester resin,which comprises (1) reacting an epoxy resin having an average of greaterthan one vicinal epoxy group with a phosphoric acid source materialselected from the group consisting of 100 percent phosphoric acid, asemi-hydrate of phosphoric acid, a polymeric phosphoric acid, a partialanhydride of phosphoric acid, pyrophosphoric acid, orthophosphoric acid,triphosphoric acid, superphosphoric acid and a mixture thereof to obtainan epoxy phosphate ester; and (2) then adding additional phosphoric acidsource material to the epoxy phosphate ester obtained in step (1); and(3) further reacting the epoxy phosphate ester obtained in step (1) withthe additional phosphoric acid source material.
 2. A process accordingto claim 1, wherein in the first reaction the epoxy resin is reactedwith a phosphoric acid source material in an amount to provide fromabout 0.2 to about 0.4 hydroxyl group per epoxy group; and in the secondreaction the obtained epoxy phosphate ester is reacted with a phosphoricacid source material in an amount to provide from about 0.05 to about0.4 hydroxyl group per epoxy group.
 3. A process according to claim 1,wherein each of the first and second reaction are carried out at 50° C.to 150° C. for a period of from 1 to 110 minutes.
 4. A process accordingto claim 1, which further comprises subjecting the epoxy phosphate esterresin obtained to hydrolysis treatment with water to produce an epoxyphosphate monoester; and then subjecting the obtained epoxy phosphatemonoester to neutralization treatment.
 5. A process according to claim1, wherein the epoxy resin is a glycidyl ether of bisphenol A, glycidylether of bisphenol K, glycidyl ether of bisphenol F, glycidyl ether ofbisphenol S, glycidyl ether of bisphenol AD or a mixture thereof.
 6. Anepoxy phosphate ester resin prepared by the process of claim
 1. 7. Acoating composition comprising:(a) the epoxy phosphate ester resin ofclaim 6; (b) an acrylic resin or a polyester resin, miscible with theepoxy phosphate ester resin; (c) at least one curing agent; and (d)water.
 8. A coating composition comprising:(a) the epoxy phosphate esterresin of claim 6; (b) an acrylic resin or a polyester resin, misciblewith the epoxy phosphate ester resin; (c) at least one curing agent; and(d) an organic solvent.
 9. The epoxy phosphate ester resin of claim 6which is water-soluble.